The invention relates to rotary pneumatic tools, and more particularly to such tools which employ a governor to control the speed of the motor.
In rotary pneumatic tools, it is desirable to prevent overspeeding of the motor, particularly when the tool is used to rotate a grinding wheel. The operating speed of such a tool is generally controlled by a centrifugally operated governor which throttles down the flow of air to the motor in response to the attainment of a specified operating speed. This main governor can malfunction for a variety of reasons, including the presence of wear, dirt, rust, air line moisture which may condense and freeze in the tool, or improper lubrication of the tool. Such malfunctions prevent the desired speed control, so that the tool can quickly exceed the safe speed of rotation of a grinding wheel. The resulting centrifugal force will cause the grinding wheel to disintegrate, posing a danger of serious injury and damage.
To prevent the overspeeding of such rotary pneumatic tools, various overspeed regulators and shutoff devices have been suggested. See, for example, U.S. Pat. Nos. 2,422,733, 2,586,968, 3,002,495, 3,043,273, 3,071,115, 3,257,913, 3,279,485, 3,519,372, 3,587,752 and 3,749,530. In operation, the overspeed devices generally rotate with the motor shaft and are activated in response to centrifugal forces above those associated with the intended operating speed of the tool. The overspeed devices generally shut off air supply to the motor, stopping the tool, and are often designed to remain in the shutoff position until the tool is dismantled to enable resetting of the device. In this way, repair of the defect which caused malfunction of the tool's speed governor is encouraged.
The tools referenced above utilize various structural arrangements to accomplish their common objective. In some of the arrangements certain shortcomings are inherent. For example, in devices which utilize a "frictionless" type movement of the overspeed device (comprising a deflectable spring washer) into the shutoff position, problems are inherent with the manner in which the device is rotatably driven. The frictional engagement of an annular rubber grommet is depended upon to drive such a device. Deterioration of the grommet can result in failure of the overspeed device to rotate at motor speed and consequently to prevent overspeeding of the tool. Also, virtually all of the referenced devices are unprotected from contaminants such as hose residue, pipe scale and other foreign material which can cause malfunction of the overspeed device as well as of the operating speed governor.